1. Field of the Invention
The present invention relates to a method for transferring quality declaration data in an ATM (asynchronous transfer mode) network.
2. Related Arts
In recent years, multimedia services have been making rapid progress, and accordingly demands for an ATM switching and system are increasing. ATM technology enables efficient transmission of multimedia information in high speed with a guaranteed communication quality for information contents.
Quality control is attained in the following manner in case of SVC (switched virtual connection)—a switching method of selecting channel to the destination and setting up connection thereto. When setting up a connection, an originating user declares a desired communication quality to an ATM switching. There are provided a quality control principle and a procedure for declaring quality control information standardized by ITU-T (International Telecommunication Union's Telecommunication Standardization Sector) or other organizations such as the ATM forum for establishing necessary recommendations. Through this procedure, quality control according to declared contents is realized.
Efforts for standardization conducted by the above organizations started in 1993. Since then, a lot of works have been brought about to improve the recommendations in various points. Such improvement is triggered by increased variety of multimedia services and expanded use of ATM switching technology. Quality control technology itself has also been improved.
As a result, the recommendations have changed to supplement the initial recommendation and, in addition, new recommendations have been established. Accordingly, the contents have greatly been modified from the initial recommendation.
This tendency is remarkable especially in quality control issues which act as one of the major roles among ATM technologies. Although the situation surrounding ATM has been changed as described above, most equipment for ATM control used today respectively for data originating point, data terminating point and data transfer equipment is based on the initial recommendation.
From now on, it is expected that the market will further expand by implementing up-to-date control method based on new recommendations to achieve more efficient transmission, as well as by introducing refined QoS (quality of service) control corresponding to each transmission contents.
Improvement of quality control incorporated in the related recommendations has aimed at the same target of quality control principle. However, actual approaches to the targeted control principle are different, and at present the improvement of control principle succeeds these differences. Under such circumstances, variations in these recommendations as well as the versions established for supporting data originating point, for receiving point and for ATM network become more and more apparent.
It is not desirable if the above phenomenon brings about impeding the uniformity of communication quality for end-to-end connection (connection between user terminals) of data transmission.
The current versions of the established recommendations and the differences thereof are summarized below. Also, problems which may occur at the time of establishing connections are pointed out.
Recommendation (1): ITU-T SCS1—specifying QoS=0 only.
A user cannot designate specific quality requirement. The quality accords to the quality determined by the ATM switching based on the declaration data of traffic information and bearer information, which is not the declaration of QoS (quality of service).
Recommendation (2): ITU-T SCS2—specifying QoS=1 to 4.
With this Recommendation, specific QoS control becomes possible by a user. When QoS=0 is declared, the control same as the recommendation (1) is carried out. When either of QoS=1 to 4 is declared, quality of service is specified based on the declared QoS information.
Recommendation (3): ATM forum V3.1 IISP (Interim Inter-Switch Signaling Protocol)—specifying QoS=0, 1 to 3.
The control same as the recommendation (1) is carried out irrespective of QoS value. However, the declared QoS is treated as auxiliary information. Further, the declaration of auxiliary information is specified to realize traffic quality expected when QoS=0. When traffic type UBR is desired, “best-effort” indication is added in traffic declaration data of QoS=0. Recommendation (4): ATM forum V4.0—specifying QoS=0, 1 to 3.
In addition to the recommendation (3), it is possible to declare extended quality control information. It is intended to bring out the capability of ATM switching in case of traffic other than UBR (unspecified bit rate) or ABR (available bit rate). Also the ABR case is specified as well as UBR. When traffic type ABR is desired, the declaration of QoS=0 is mandatory.
As may be appreciated by the above description, different contents are specified by the various recommendations. This causes the following problems which result in impediments to interwork communications between users where different recommendations and/or versions are applied respectively.    (a) Difference between the recommendations of subscriber support protocol and/or the versions.            When the different recommendations and/or versions are used for subscribers accommodated in an ATM switching for their respective purposes, there may be a case that QoS indication does not coincide each other. For this reason, when originated information is transferred to a destination user without modification, connection setup request may be rejected because the declaration is treated as undefined or is unsupported, thus the interworking is impeded.        The interworking between the recommendations and versions explained above is summarized in the following table.        
InterworkingOccurrence ofInterworkingOccurrence ofrelationsimpedimentrelationsimpediment(1)→ (2)◯(3)→ (1)Δ4→ (3)◯→ (2)Δ5→ (4)◯→ (4)◯(2)→ (1)Δ1(4)→ (1)Δ6→ (3)Δ2→ (2)Δ7→ (4)Δ3→ (3)Δ8Explanatory notes:◯: No impediment occurs.Δ: Impediment occurs partially.Δ1: QoS declaration is not permitted, except QoS = 0.Δ2: Declaration of QoS = 4 is not permitted.Δ3: Special condition exists (as shown in (2) and (3) below.)Δ4: Declaration is not permitted, except QoS = 0.Δ5: Special condition exists (as shown in (2) below.)Δ6: Declaration is not permitted, except QoS = 0. Also, declaration of extended information is not permitted.Δ7: Declaration of extended information is not permitted.Δ8: Declaration of QoS = 4 is not permitted. Also declaration of extended information is not permitted.    (b) Different control in spite of identical QoS declaration value specified.            As shown below, even when the identical QoS value is declared, the permitted traffic types are different, resulting in the impediment of interworking.        QoS=4 in the above recommendation (2) corresponds to the traffic type UBR, while        QoS=4 in the above recommendation (4) corresponds to the traffic type nrt-VBR (non-real-time variable bit rate).        Therefore, it is not possible to inform QoS information between subscribers respectively supporting the above two recommendations, so far as the original value is transmitted.            (c) Different QoS value declaration on desired traffic type.            As explained below, permitted QoS values differ depending on desired traffic types, which impedes interworking.                    1) To desire traffic type UBR, QoS=4 is specified to declare in case of the recommendation (2) on the other hand, QoS=0 is specified and additionally best-effort information is attached thereto in case of either the recommendations (3) or (4).            2) To desire traffic type ABR, QoS=3 or 4 is specified to declare in case of the recommendation (2), while QoS=0 is specified in case of the recommendation (4).                            (d) Difference on receivable QoS information, producing failure to transfer necessary information.            When a detailed request other than QoS is issued based on the extended quality control information specified by the ATM forum V4.0, there may be a case that the above request information cannot be transferred to a destination user accommodated in an ATM switching, in the case the communication protocol does not conform to the recommendation or version in which the aforementioned information is supported. Moreover, the declaration of QoS is not necessary when the extended information is declared. This further impedes interworking.            (e) Accurate information exchange not possible even between ATM switchings, especially in the case of interchange between the ATM switchings manufactured by different manufactures.            For example, there may be a case that the declaration QoS=0 is unconditionally controlled as a UBR traffic. Therefore, even QoS=0 is declared, uniform quality control is not always provided through an end-to-end connection.        